Dry Lining and Steel back boxes - Sealing

From what I have read seems new builds need such boxes sealing for against fire/smoke spreading.

On my existing 1980s house it was originally all metal boxes but have had some dry lining plastic boxes added over the years.

The original metal boxes could not be said to be air tight due to so many wires coming in to the light switch boxes , as the original builders/electricians used them as the junction box; and also notice some unused knockouts simply missing and fully exposing the void in the stud walls.

With the dry lining boxes, well so many large openings, but no sealer or grommets were used on them.

While think such sealing would not be a requirement to old existing installations, I would like to seal them while replacing the fittings, for my own peice of mind and safety, but unsure what is the correct / easiest material to use to retro seal all these gaps ?

Seen other web comments about just using plaster on new walls or an acrylic sealer on existing boxes, as simple as that ... ??

ricky101 said:

From what I have read seems new builds need such boxes sealing for against fire/smoke spreading.

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Where did you read that?

Do you have any reasons for believing that whoever wrote it knows what they are talking about?

The original metal boxes could not be said to be air tight due to so many wires coming in to the light switch boxes , as the original builders/electricians used them as the junction box; and also notice some unused knockouts simply missing and fully exposing the void in the stud walls.

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Indeed.

And do you see that as a fire risk?

While think such sealing would not be a requirement to old existing installations, I would like to seal them while replacing the fittings, for my own peice of mind and safety, but unsure what is the correct / easiest material to use to retro seal all these gaps ?

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Something fireproof, I guess. Make sure it doesn't damage the insulation on the cables, and think about its thermal performance in case you need to put larger cables in.

Seen other web comments about just using plaster on new walls or an acrylic sealer on existing boxes, as simple as that ... ??

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Is acrylic sealer fireproof?

Seals are required to prevent air leakage, not for fire prevention.
Some info: http://www.nhbc.co.uk/ProductsandServices/ConsultancyandTesting/Airleakageservices/Faqs/
which is all part of the obsession of making building totally air tight and sealed so that the occupiers can save 0.1% on their heating bills.

Well those savings will come in jolly useful. They can be used to pay for the sponges, buckets and mildew remover.

It saves a tad more than that, FP.. Building to the passivhaus levels of air tightness and insulation (which aren't stellar by the way, 0.6 of the house volume per hour and 0.15 u of the walls) combined with orienting the house properly to acquire heat from the sun means the heating bills are £0 per year

BAS, you do know that air tight houses necessarily have controlled mechanical ventilation systems, right? They don't suffer from condensation, mould or poor air quality

ban-all-sheds said:

ricky101 said:

From what I have read seems new builds need such boxes sealing for against fire/smoke spreading.
Where did you read that?

Do you have any reasons for believing that whoever wrote it knows what they are talking about?

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Please do not laugh out too loud, but it was one of those big Red books - the Collin DIY manaul, like these old Readers Digest books, saying to seal and must also use blind grommets, not the open ones.

The original metal boxes could not be said to be air tight due to so many wires coming in to the light switch boxes , as the original builders/electricians used them as the junction box; and also notice some unused knockouts simply missing and fully exposing the void in the stud walls.
Indeed.

And do you see that as a fire risk?

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Well when the socket or switch is removed you can feel a draught sometimes, so would seem reasonable that it could be a way for smoke and fire to travel easily; though expect by then the whole stud partition would be on fire anyway ...

While think such sealing would not be a requirement to old existing installations, I would like to seal them while replacing the fittings, for my own peice of mind and safety, but unsure what is the correct / easiest material to use to retro seal all these gaps ?

Something fireproof, I guess. Make sure it doesn't damage the insulation on the cables, and think about its thermal performance in case you need to put larger cables in.


Seen other web comments about just using plaster on new walls or an acrylic sealer on existing boxes, as simple as that ... ??
Is acrylic sealer fireproof?

Click to expand...

Since I posted had seen things like Intumescnet Sealers n both Acrylic and ilicone which the makes say are wiringsafe and also things like putty pads for the boxes.

However from the jist of your reply, basically its not a wiring regs requirement, new build or existing, to air tight seal the back boxes ..?

Air tight sealed houses, 25 years ago: https://goo.gl/bDs8Bb

ricky101 said:

Please do not laugh out too loud, but it was one of those big Red books - the Collin DIY manaul,

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Certainly won't laugh - on the whole books like that are pretty good.

like these old Readers Digest books, saying to seal and must also use blind grommets, not the open ones.

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But are you sure they were saying that for fire stopping, not draughts or condensation?

Well when the socket or switch is removed you can feel a draught sometimes, so would seem reasonable that it could be a way for smoke and fire to travel easily; though expect by then the whole stud partition would be on fire anyway ...

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Possibly.

Assuming you live in a 2-storey house, I invite you to go into your hallway and look up at the sodding great hole which runs from the ground floor to just below the loft, and think about easy paths for fire and smoke.

Since I posted had seen things like Intumescnet Sealers n both Acrylic and ilicone which the makes say are wiringsafe and also things like putty pads for the boxes.

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My apologies - when you said "acrylic" I thought you were talking about some kind of coating.

However from the jist of your reply, basically its not a wiring regs requirement, new build or existing, to air tight seal the back boxes ..?

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No, it is not a WR requirement. It may be necessary to meet BR requirements for airtightness or preventing interstitial condensation.

cjard said:

BAS, you do know that air tight houses necessarily have controlled mechanical ventilation systems, right? They don't suffer from condensation, mould or poor air quality

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And when the ventilation system breaks down ? Or there is a power cut ? The answer is that windows have to be opened to ensure ventilation. But the heating system depends on the heat recovery built into the mechanical ventilation system. The minimal heating sources are inadequate to keep the house warm when there is heat going out of the windows.

One of the best "design features" is having the letter box on a post outside the house. Hence there is no draught inducing letter box in the front door. But the whole front door has to be opened to go out and see if there are any letters. No doubt this will be dealt with by having air lock system behind the front door.

Same thing that happens when your washing machine breaks down; you repair it or replace it and life goes on. In the mean time, you can make do with some uncontrolled ventilation and if it's cold, you plug in a fan heater/light the gas fire/hob ring

It's a fan in a box, it doesn't really get much simpler so there isn't a lot to go wrong. if these things broke down left, right and centre then I'd agree but all in, they just don't.. No one buys a boiler wih the approach of "but what if it breaks down in the dead of winter? We'll die of hypothermia!" they just fit an electric shower and a Quooker, and a generator if they're that paranoid

Ps, air tight doesn't mean the house is a Tupperware tub and spending 8 hours in it with a failed vent system means you suffocate.. The passivhaus limit for air changes by fabric permeation is 0.6 times the volume of the house so even passivhauses leak from the fabric. They probably are the other end of the spectrum from a 500 year old cottage though

The sales rep for the eco houses being built nearby was full of praise for them. But when asked if he would choose to live in one he declined to answer. His answer to power cuts was "open a window" but he thrn declined to become involved with discussions about heating with a window open.

cjard said:

and if it's cold, you plug in a fan heater/light the gas fire/hob ring

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The fan heater wouldn't work in a power cut. Some of these houses may not have a gas supply as they do not need that much heating. And using the gas hobs in a sealed building will use up oxygen and create condensation.

My understanding is that in the extreme these houses are required to be so air tight as to be pressure tested to ensure there are no leaks. If the design considers that a letter box is too leaky to be in the front door then permiability through the fabric will have been reduced to an absolute minimum as well.

bernardgreen said:

One of the best "design features" is having the letter box on a post outside the house. Hence there is no draught inducing letter box in the front door. But the whole front door has to be opened to go out and see if there are any letters. No doubt this will be dealt with by having air lock system behind the front door.

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We could call it a porch

Oh Bernard, for someone who normally delivers such rational, reasonable and well thought out posts you sure are making a big deal of an event that happens so seldom and with such minimal overall impact that I wonder if there's a slight flaw in your understanding of low energy housing

A passivhaus has the luxury of being able to operate like a draughty 60's semi should the need arise in the 0.01% of the time chance occurrences like a power cut come along. The energy requirements of a PH are so low that it's feasible to run it off an emergency power source in such situations. You'll note of course that the reverse is not true (and thus you'll be worse off in that semi whose combi boiler is powerless/failed). I also refer you to my earlier point about misuse of the phrase "airtight" which might lead people to think that passivhauses are like Tupperware tubs. They aren't.

If you take a dim view of anything that is engineered and powered by finely balanced fallible technologies then I'd ask you if you would really return to a world full of carbureted cars belching out plumes of unburnt leaded four star, and vote to replace every combi boiler in London with a coal fire. Perhaps you were there also, at the introduction of closed loop fuel injection systems asking the sales rep "what if the ecu fails and the engine stops in the middle of a motorway?" or "what if the boiler PCB burns out and Mrs Miggins doesn't have any heating?"

But, probably not

I agree that modern technology brings many benefits, especially in the matter of reducing polutants from internal ombustion engines. But failure of the high tech systems in vehicle is a fact of life. Over complicated steering lock on a car ( has its own micro-processor and talks to main ECU via CanBus ) strands a motorist when the CanBus driver fails. ECU cannot get verification the steering is un-locked so will not allow the car to be started. Similar with window motors, the car will start but has to be parked with the faulty window left open. But it makes assembly of the car much cheaper and passes cost onto the owner in repair bills.

Back to houses. In the 1970's I took a deep interest in the Philips Experimental House at Eindhoven and the Autonomous House Project ( TV series created around it ) in the UK ( Birmingham ? ) and other Eco houses as we were about to self build a house. A lot of the problems and dis-advantages of eco living were identified in those projects. Many of them have never been fully resolved even now 40 year later. An aquaintance and her partner built a super eco house on one of the Milton Keynes "Future Homes Projects " ( they designed it and then employed builders to build it ). Within a year they had drastically re-designed the systems it as it was "not an easy house to live in" and later sold it at ( I am informed via rumour ) for a price significantly less than the cost of building it.

I take a dim view of complex technology being sold for profit when simpler technology will perform the task equally well and can be serviced without the need for complex equipment and highly trained ( ? ) technicians.

So often we see solutions in search of a problem.